JP2004517489A - Systems and methods for electrically induced breakdown of nanostructures - Google Patents

Abstract

A method is provided for forming a device. The method provides a substrate, and provides a plurality of nanotubes in contact with the substrate. The method comprises depositing metal contacts on the substrate, wherein the metal contacts are in contact with a portion of at least one nanotube. The method further comprises selectively breaking the at least one nanotube using an electrical current, removing the metal contacts, cleaning a remaining nanotube, and depositing a first metal contact in contact with a first end of the nanotube and a second metal contact in contact with a second end of the nanotube.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to nanostructures, and in particular, to systems and methods for electrically induced breakdown of nanostructures.
[0002]
[Prior art]
In the field of molecular nanoelectronics, few materials are as promising as nanotubes, especially carbon nanotubes, which include hollow cylinders of graphite several Angstroms in diameter. Nanotubes can be made into small electronic devices such as diodes and transistors according to their electrical properties. Nanotubes have unique sizes, shapes and physical properties. The structure of carbon nanotubes resembles a hexagonal lattice of carbon wound into a cylinder.
[0003]
Besides exhibiting interesting quantum behavior at low temperatures, carbon nanotubes exhibit at least two important properties. Nanotubes can be metallic or semiconductive depending on their chirality (ie, conformational geometry). Metallic nanotubes can carry very high current densities at a constant resistivity. Semiconductive nanotubes can be electrically switched on and off as field effect transistors (FETs). The two types can be covalently joined (shared electrons). These properties indicate that nanotubes are an excellent material for making nanometer-sized semiconductor circuits.
[0004]
Current methods of studying nanotubes rely on the random formation of metallic and semiconducting nanotubes. There is no known method for producing nanotubes having specific characteristics with high reliability, and there is even less known a method for producing nanotubes exhibiting a junctional behavior such as transistors, diodes, and the like. Also, there has been no known method of separating nanotubes by selective synthesis or post-synthesis with a certain success. Until now, nanotubes had to be individually separated from a mixture of metallic and semiconducting nanotubes or randomly placed on the electrode under study. However, there is no notable consistency in such a method.
[0005]
[Problems to be solved by the invention]
This lack of control, combined with the tendency for nanotubes to be bundled, has hindered the physical study of nanotubes, and has been seen as a major impediment to nanotube development, including nanotube-based electronics. I have. Accordingly, there is a need for a system and method for producing nanotubes having desired properties.
[0006]
[Means for Solving the Problems]
Accordingly, the present invention provides a device forming method including providing a substrate, forming a plurality of nanotubes in contact with the substrate, and selectively destroying the nanotubes using an electric current. Preferably, the method further comprises the step of depleting the carriers of the semiconductive nanotube.
[0007]
Preferably, the step of depleting the plurality of carriers of the semiconducting nanotube further comprises applying a voltage to a gate electrode on the substrate. Preferably, the method includes passing a current from the source electrode to the drain electrode through the nanotube.
[0008]
Preferably, the plurality of nanotubes are multi-wall nanotubes, including metallic and semi-conductive nanotubes. Preferably, selectively destroying the method comprises destroying an outer metallic nanotube.
[0009]
Preferably, the plurality of nanotubes are single-walled nanotube ropes including metallic and semi-conductive nanotubes, and the breaking comprises breaking at least one metallic nanotube.
[0010]
Preferably, the nanotubes are provided in a density between the monolayer and 1/10 percent coverage.
[0011]
The substrate is an insulator and preferably includes an array of metal pads.
[0012]
The substrate is a silica-based substrate and preferably includes a metal pad array.
[0013]
Each pad preferably includes one of a source electrode, a drain electrode, and a gate electrode.
[0014]
The step of providing a substrate is performed by forming a pad array using lithography, with each pad preferably including a corresponding electrode on an insulating substrate.
[0015]
Preferably, the nanotubes are carbon nanotubes.
[0016]
Preferably, the method further comprises destroying the plurality of stray nanotubes.
[0017]
According to another aspect, the invention is a method of modifying at least one property of a nanotube, comprising providing a mixture of nanotubes, and passing an electrical current through the mixture to induce selective destruction of the nanotube mixture. And a method comprising: Preferably, the method further comprises the step of removing carriers from the semiconductive nanotube.
[0018]
Preferably, the current selectively destroys the metallic nanotube. Preferably, the power applied to the mixture is about 500 μW.
[0019]
Preferably, the nanotube is one of a multi-wall nanotube and a single-wall nanotube rope.
[0020]
Preferably, the characteristic is one of diameter, density and conductance.
[0021]
Preferably, the mixture comprises metallic and semiconductive nanotubes.
[0022]
Current density is 10 ⁹ A / cm ² It is preferably larger than.
[0023]
According to another aspect, the present invention provides an insulating substrate including a source electrode, a drain electrode and a gate electrode, forming a carbon nanotube bundle comprising metallic and semiconductive component nanotubes in contact with the substrate. The nanotubes are provided at a density of about 1 percent coverage, and the present invention further applies a voltage to the gate electrode to deplete the carriers of the semiconductive component nanotubes and to pass a current from the source electrode to the drain electrode through the nanotube. A method for forming a device for flowing and destroying at least one metallic component nanotube to form a field effect transistor is provided.
[0024]
Preferably, the carbon nanotube bundle can be a multi-wall nanotube or a single-wall nanotube rope.
[0025]
Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, there is provided a method for permanently modifying multi-walled nanotubes (MWNT) or single-walled nanotubes (SWNT) ropes or bundles. Nanotubes can be metallic or semiconductive, depending on their chirality (ie, conformation). Both types are found in MWNT and SWNT. The method according to the present invention uses current-induced electrical breakdown to remove individual nanotubes with specific properties. This method can tune the properties of composite nanotubes by changing the percentage of component nanotubes. Although the present invention is described using carbon-based nanotubes, it is noted that the methods illustrated herein are applicable to any molecular structure that can selectively apply an electric current to a particular surface. I want to be. For example, the invention can be used with boron nitride (BN) and metal dichalconide (MX2) based nanostructures.
[0027]
Carbon nanotubes are 10 ⁹ A / cm ² Can withstand current densities exceeding. This is in part due to the strength of the carbon-carbon bonds (eg, the bond strength of one CC bond is about 347 kJ / mol). Ultimately, however, the nanotubes will be destroyed by a sufficiently large current. For example, in MWNTs, breakdown in air occurs at some threshold power, eg, about 500 μW, at higher powers a rapid oxidation of the outermost carbon shell begins. Power is equal to current multiplied by the potential difference (ie, voltage). Since the thermally induced oxidation of defect-free graphite proceeds only at very high temperatures, for example> 2000 ° C., the main factor in the initiation of breakdown according to the invention is current-induced defect formation, and self-heating has a second effect. It is.
[0028]
Please refer to FIG. The nanotubes 102 include a hexagonal lattice of carbon or other molecules. In the case of carbon, a ring 104 containing six carbons covalently bonded together is constructed. FIG. 2 shows the individual carbocycles. Each intersection 106 represents an individual carbon atom and the bond is shown at 107. One alternative structure is a boron nitride ring, one form of which is shown in FIG. The boron nitride ring can include three nitrogen atoms, for example, 110, alternately bonded with three nitrogen atoms, for example, 110.
[0029]
By utilizing current-induced defect formation, the method according to the present invention selectively destroys nanotubes that are carrying current. If the parallel nanotubes carry little or no current, they have no effect. For example, in the MWNT shown in FIG. 4, the outermost shell 102 is selectively destroyed. This is because the shell is in direct contact with external electrodes (eg, source and drain). This current distribution protects the innermost shells that carry little or no current during current-induced oxidation, which remains behind. In the SWNT rope shown in FIG. 5, individual nanotubes (eg, 102) are arranged in parallel. The distribution of the current through the SWNT rope is more uniform than the distribution of the current through the MWNT, since the individual nanotubes of the SWNT rope can form a good contact at the same time as the external electrodes.
[0030]
In general, there is no reason for current to flow preferentially through one SWNT over another, but according to one embodiment of the present invention, the carrier of the component semiconducting nanotube is provided by an electrostatically coupled gate electrode. Can be selectively depleted. In other words, in a SWNT or MWNT applied between a source electrode and a drain electrode, carriers can be depleted from the component semiconductive nanotube by applying a voltage to the corresponding gate electrode. After depletion, the semiconducting nanotubes are protected from damage and the high current density applied to the SWNT or MWNT by the source electrode can be used to initiate oxidation of the component metallic nanotubes. Thus, these methods can protect the semiconductive nanotubes of the SWNT rope, as well as the outer semiconductive shell of the MWNT.
[0031]
Removal of carbon nanotubes from these composite conductors can be observed both electrically and microscopically. Electrically, the destruction of a single carbon nanotube results in a partial decrease in conductance, which is typically completed in a matter of milliseconds. Stressing with a sufficiently high bias causes multiple independent drops as the carbon shells break down one after another. The electronic circuitry used in this destruction can control the number of destructed nanotubes. Upon sensing a current drop, eg, about 19 μA, the electronics can interrupt the breakdown process and control the characteristics exhibited thereby.
[0032]
Referring to FIG. 6, the partial electrical breakdown of the MWNT under constant voltage stress proceeds in a series of discrete steps corresponding to the loss of individual layers of the eight-layer MWNT. These results were obtained at a power of about 450 μW and a potential difference of about 2 volts. FIG. 6 also shows a regular breakdown with a current of about 19 μA per shell. The radius reduction of the partially broken MWNT is equal to the spacing between shells (0.34 nm) multiplied by the number of completed breaking steps. Similar thinning can be achieved with SWNT bundles, with metallic SWNTs selectively destroyed, leaving only semiconductive SWNTs.
[0033]
Since relatively small electric fields and currents affect individual molecules, the sensitivity of the nanotubes to external stress assists in this destruction. For example, 1 nm diameter semiconductive nanotube electrical carriers can be electrostatically depleted by gate electrodes several hundred nanometers apart. The current density (current density sufficient to affect the destruction of the nanotube) acts as a catalyst to initiate a chemical reaction between the nanotube and the surrounding gas. For example, for a carbon nanotube in air, the reaction can be written as: C (nanotube) + O ₂ (Gas) → CO ₂ (gas).
[0034]
The present invention further contemplates other environments in which certain nanotubes can be chemically modified by current-assisted non-destructive reactions. The resulting device could incorporate both electrical switching and chemical sensitivity. For example, using the sensitivity of nanotubes to various gases, this chemical modification can be used in the context of chemical nanosensors, where a change in the conductivity of the nanosensor (nanotube) signals the presence of a particular gas.
[0035]
The controlled destruction of nanotubes can separate semi-conductive SWNTs from a mixture of SWNTs (including metallic and semi-conductive SWNTs) and produce nanotube-based field effect transistors (FETs). Also note that using the methods disclosed herein, transistors (eg, FETs), diodes, and resistors can be manufactured depending on the properties of the nanotubes and the design of the substrate.
[0036]
Basically, this process facilitates the study of the complex electronic structure and transport properties of MWNT and SWNT ropes. By removing the stress (current) at the individual conductance steps, the properties of these composite nanowires can be re-evaluated after loss of the respective constituent conductor (nanotube). This characterization refers, for example, to the conductance characteristics of the MWNT or SWNT rope from one stage of the fracture process to another. A plurality of complementary transport measurements can, for example, probe deeper into the shells inside the MWNT, allowing characterization as well as direct comparison of transport through each shell.
[0037]
In MWNTs, it is assumed that the metallic shell and the semiconductive shell occur alternately at random. This can be tested directly by using controlled breakdown, followed by performing a low bias or low temperature measurement that examines the outermost shell of the MWNT. According to the previous measurement for SWNTs, a distinction can be made between semiconductive and metallic shells by measuring the conductance G to the gate voltage Vg using a relatively small source-drain bias of 10 mV. Metallic shells feature G independent or nearly independent of Vg, while semiconductive shells can electrostatically deplete carriers by the gate.
[0038]
Please refer to FIG. By stopping the stress during each failure event, the properties of the MWNT can be evaluated after each loss of the constituent shell. FIG. 7 shows the low bias conductance (G (Vg) between semiconducting (eg, 402 and 406) and metallic (eg, 404) behavior due to the charging properties of the outermost shell at each breakdown stage. )). In FIG. 8, when the last metallic shell (n-9) is removed, the remaining semiconductive shell can be completely depleted to obtain a region of zero conductance. Taking the G (Vg) peaks indicated by the arrows corresponding to the conductance and valence band edges, the band gap of the different shells can be determined as a constant or a proportional relationship. This relative width is consistent with the calculated result based on the expected diameter dependence, as shown in FIG. This calculation is only parameterized by the initial diameter of the tube and the spacing between adjacent shells of 0.34 nm.
[0039]
FIG. 7 shows G (Vg) at room temperature for various different layers of MWNT. MWNTs initially have a diameter of 9.5 nm, an n-layer shell and metallic G (Vg). FIG. 7 shows the strong modulation of G (Vg) 402 observed after removal of the three shells. Removing the fourth layer results in metallic G (Vg) 404, and removing the sixth shell results in another semiconductive G (Vg) 406. This variation is interpreted as representing the interchangeability of the properties of the carbon shell being removed.
[0040]
The reason that G does not drop to zero for a particular semiconductive shell is due to the contribution of the inner metallic shell that remains conductive. Shells n-3 and n-4 prove this. The minimum value of depletion in the G (Vg) curve of shell n-3 is consistent with the conductance of shell n-4 408 below. In this case, the outer semiconducting shell n-3 is completely depleted by the gate, but the measured conductance includes leakage through the underlying metallic shell. According to additional measurements, the leak is frozen at low temperatures, and this low bias limit indicates that the bond between the shells is activated by heat. The progressive thinning of the MWNT and SWNT ropes can be resolved using, for example, nuclear and scanning electron microscopy, with a linear correspondence between the number of failure steps and the change in apparent diameter.
[0041]
Upon removal of the tenth carbon shell, the MWNT begins to behave like a perfect intrinsic field effect transistor (FET) having a region of zero conductance due to complete depletion of carriers even at room temperature (eg, (FIG. 8). Similar properties are found with individual semiconductive SWNTs. However, the SWNT used was a strong p-type and did not show symmetric G (Vg) characteristics. Complete depletion of the MWNT indicated that no metallic shell remained, and this behavior continued until the 14th carbon shell was removed, at which point the MWNT circuit was open. Based on the known shell-to-shell spacing of approximately 0.34 nm, the number of shells for a MWNT of this diameter is at most 14, which is consistent with the per-shell count.
[0042]
FIG. 8 shows the progressive increase in the zero conductance region when the last semiconductive shell is removed. The width of this region is proportional to the band gap of the semiconductor (the energy required to break the bond), and conduction above and below this gap is due to electron and hole-like carriers, respectively. Because high voltage pulses are used to break the shell, the rearrangement of the trapped charge causes the underlying SiO 2 ₂ Happens on the substrate. To simplify the comparison between shells, the curve shown in FIG. 8 has its center near Vg = 0. A characteristic of semiconducting carbon nanotubes is that the band gap energy is inversely proportional to the diameter, so a smaller carbon shell shows a larger band gap, and the width of the band gap depends on the type of material (conductor, Semiconductor, insulator). Using only the initial diameter of the MWNT and the spacing between the shells, the ratio between the expected band gaps of the innermost shells can be calculated. As shown in FIG. 9, these ratios are consistent with the experimental ratios shown in FIG. 9 defined by the conductance peaks on either side of the conductance gap.
[0043]
Next, reference is made to FIG. By re-evaluating the properties of the MWNTs after individual shell losses, the contribution of each shell to IV can be determined. Based on a series of uniformly spaced IVs, each shell saturates with the same current and all shells contribute to conduction at medium and high bias. The dashed line indicates the position of IV that was not obtained. The semi-log plot of the selected IV indicates that the IV tends to be exponential due to the effective barrier between these and the outer electrodes in the innermost shell group. A similar barrier probably plays a role in all but the outermost shell, explaining the nonlinearity observed with some MWNTs.
[0044]
FIG. 10 shows a series of high bias voltage-current characteristics (IV) that effectively re-evaluate the characteristics of a MWNT having shells such as n, n-1, n-2, etc., until only a single shell remains. . A high bias IV must be obtained in a high vacuum, for example, a vacuum of <1 mbar or an inert environment to suppress destructive oxidation. The MWNTs were exposed to air between each curve to controllably remove a single carbon shell. In order to monitor the contact resistance (Rc) to each nanotube, 4-probe measurements and 2-probe measurements were periodically compared. The data shown is for a sample that exhibits a constant Rc of several kilohms through this series of measurements. Samples with high Rc tend to break at the point of contact, contrary to the per-shell mechanism described herein. Each IV shows a similar current saturation as observed for individual SWNTs with increasing bias, but the current is much higher. Removal of each shell from the MWNTs appears to reduce this saturation level by a fixed amount of about 20 μA, consistent with FIG. This gradual decrease indicates a high bias, clearly indicating that all MWNT shells contribute equally to transport and saturation.
[0045]
In addition to decreasing the current saturation value, the series IV in FIG. 10 shows an increase in non-linearity when the shell is removed. The semi-log plot of the selected IV is from the linear IV to I = A exp (V / V _o ), V _o = 0.50V shows a tendency toward exponential function characteristics. Apparently, the tunneling barrier dominates the IV of the innermost shell group. This is probably because these shells can only be bonded to external electrodes through a barrier consisting of many graphite layers. In the middle shell, which is not in direct contact with the electrode, qualitatively understands the anomalous shape of the measured IV due to the inherent vertical IV characteristics of the nanotube and the depth-dependent barrier in series can do. This series barrier accounts for the gradual increase in bias required to reach the current saturation shown in FIG. In addition, the transition from the linear IV to the non-linear IV observed here, and similar non-linear IVs that are well documented in the literature, indicate that transport experiments often result in current passing carbon It does not directly contact the shell, but rather suggests contact with a partial or incomplete shell commonly observed by transmission electron microscopy.
[0046]
Figures 7 to 10 confirm the variability of the MWNT shells, quantitatively refer to the coupling between these shells, and attempt to separate the contribution of one shell to the overall conductance. To date, theories and experiments have been cracked on these issues. On the one hand, MWNTs are too complex to model in theory, and on the other hand, no experiments are known that can directly probe the inner carbon shell. The controlled destruction technique introduced herein has the potential to provide new insights into the transport properties of these complex conductors. Further, MWNTs can be selectively converted between metals and semiconductors having different band gaps.
[0047]
The method described for MWNTs can be applied to SWNT ropes. Although MWNTs and SWNTs are both composite nanotubes, SWNTs show some differences. For example, multiple SWNTs of a single SWNT rope can come into contact with a potentially oxidizing environment, thus, unlike the uniform shell-to-shell failure observed with MWNTs (eg, FIG. 6). Many carbon shells can be destroyed simultaneously. In addition, the single rope SWNTs do not electrostatically shield each other as effectively as the MWNT shell. As a result, by depleting the carrier of the semiconductive SWNT, it is possible to destroy only the metallic SWNT by destruction on one rope (in this case, Vg is mainly used to deplete the carrier of the p-type SWNT). Is maintained at +10 V during stress). The carrier density of carbon-based SWNTs can be from about 100 to about 1000 electrons / μm. Another difference is that each SWNT of the small rope connects independently to the external electrode. Therefore, the total conductance G (Vg) = G _m + G _s SWNT ropes as independent parallel conductors with (Vg) can be modeled more easily than MWNTs. In the above formula, G _m Is the contribution of metallic nanotubes and G _s Is the gate-dependent conductance of the semiconducting nanotube.
[0048]
Please refer to FIG. 11 and FIG. By stressing the SWNT rope comprising a mixture of semiconductive and metallic SWNTs while simultaneously gating the SWNT bundle, the semiconductor carriers are depleted in the selective destruction of metallic SWNTs. Initial SWNT bundles 602 and 606 include both metallic and semi-conductive SWNTs, and thinned SWNT bundles 604 and 608 include a much higher percentage of semi-conductive SWNTs. Similarly, the semiconductive nanotube shell of the MWNT can be effectively insulated by depleting the carrier of the shell using methods similar to those for SWNTs. Thus, the desired properties (eg, metallic or semiconductive) can be obtained by controlling the destruction of the MWNT. The selective destruction of composite nanotubes can be explained by the relative dependence of metallic and semiconducting nanotubes on gate voltage. The conductance of metallic nanotubes shows little dependence on gate voltage, whereas the conductance of semiconducting nanotubes shows a strong dependence on gate voltage.
[0049]
Thus, as shown in FIGS. 11 and 12, at positive gate voltages, the conductance of SWNT approaches zero, and at negative gate voltages, the conductance increases as carriers are added. FIGS. 11 and 12 show G (Vg) before and after controlled breaking of two small SWNT ropes. The conductance of these undisturbed samples can be partially modulated by the gate electrode in a manner very similar to that of the MWNT. When the metallic SWNT of the rope is destroyed, the conductance G beneath it _m Drops to zero. In contrast, the degree of modulation G _s Does not change. This measurement indicates that by depleting the carrier of the semiconductive SWNT during the breakdown process, the semiconductive SWNT can be effectively protected from damage. This result suggests that there is little electronic interaction between the different SWNTs of one rope. Measuring the temperature-dependent change in G (Vg) can address this interaction problem, and determine in what energy range such an interaction, if any, is important. be able to.
[0050]
Since the semiconductive SWNTs are not affected, the G (Vg) curve shifts strictly downward according to the contribution of the metallic SWNTs. Please refer to FIG. Even very large ropes containing hundreds of SWNTs can effectively convert these samples to FETs. But in this case, G _m Stops before it reaches zero. Perhaps this is because the metallic SWNTs in the core of the rope are covered by semi-conductive SWNTs. Higher voltages are required to destroy these weakly bonded metallic SWNTs, and some surrounding semiconductive SWNTs may be sacrificed. As a result, many semiconducting channels and G _s Only ropes with a large initial modulation of> 10 μs have G _s It can be an FET of ＦＥＴ1 μs.
[0051]
Besides being useful for studying the interaction of MWNTs and SWNTs, this controlled destruction technique is extremely useful for the fabrication of nanotube-based electronic devices. To date, SWNT FETs have been manufactured individually. In general, due to very low surface coverage, at most one SWNT will have source / drain electrodes connected at this density and most potential circuits will remain unconnected, some of which will have metallic SWNTs. Embedded, others have semi-conductive SWNTs.
[0052]
Although this technique has proven useful for the initial evaluation of SWNT properties, practical applications require the reliable generation of many devices in parallel. Achieving densely packed FETs requires, for example, purely semiconductive SWNTs of sufficient density to interconnect all desired locations. Nanotubes can be provided by known techniques, such as in-situ growth by chemical vapor deposition, ex-situ growth and attachment. At high surface densities, multiple SWNTs and SWNT ropes dominated by metallic tubes that do not serve as semi-conductive channels are preferred due to variability in WNT properties. Currently, neither a method of synthesizing purely semiconductive SWNTs nor a method of separating semiconductive SWNTs from a SWNT mixture is known.
[0053]
Please refer to FIG. This figure shows a small array of independently addressable SWNT FETs manufactured using standard lithography. An array of metal pads (eg, 701) is provided, each pad including a source 704, a drain 706, or a gate electrode 702. The substrate for these pads can be any insulating material, but is preferably a silica-based substrate. This combination of the substrate and the metal pads is called a nanotube substrate. Each FET includes a source, a drain, a gate, and at least one nanotube connecting the source and the drain. Nanotubes are formed to connect each source to a corresponding drain. Next, reference is made to FIG. A gate oxide 708 separates the gate 702 from the electrodes (704, 706). The density of the SWNTs can be adjusted so that at least one rope (eg, 710) shorts each electrode set while minimizing unnecessary connections between devices. Preferably, the nanotubes have no thickness, e.g. a single wall or less than 100% coverage. According to some results, a density of less than 1 percent is sufficient to connect each source-drain pair with at least one nanotube, but even at a density as low as about 1/10 percent of the substrate, the array Can be provided for each source-drain pair. The rope between the source and drain electrodes (eg, 710) is converted to a FET by selectively destroying the metallic nanotube. On the other hand, stray nanotubes are completely removed by complete destruction.
[0054]
These ropes initially show little or no switching due to their metallic components, but can reliably achieve the final device with good FET characteristics, as shown in FIG. it can. According to some results, SWNT FETs can be produced from disordered starting materials with greater than 90% certainty. FIG. 14 summarizes the results for 32 devices incorporating one or several SWNT ropes. Prior to denaturation (e.g., 610), the conductance of the individual ropes is extensive due to rope size distribution and contact effects, and substantially very few devices can be depleted by the gate.
[0055]
Upon destruction of the metallic SWNTs, the conductance of each rope decreases and the remaining channels become only semi-conductive, allowing the carriers to be completely depleted. The resulting device has modest FET characteristics limited primarily by contact resistance. Contact resistance is being addressed separately. Multiple small SWNT bundles can be produced by chemical vapor deposition, which can reduce the difficulties encountered with large bundles, resulting in FETs with excellent conductivity and switching ratio.
[0056]
Although the present application focuses on specific carbon nanotube systems, the same principles can be widely applied to various molecular electronics systems. In general, molecular device arrays can be created by design using external electrical means without the need for actual control at the nanometer scale. By varying the discretion, useful electronic components can be defined from random mixtures. Although this solution has been applied to solving the problem of variability inherent in carbon nanotubes, those skilled in the art in view of the present disclosure will achieve similar results using mixtures of other molecules. I can do it.
[0057]
While embodiments of systems and methods for fabricating carbon nanotubes and nanotube circuits using electrical breakdown have been described, it should be noted that modifications and variations can be made by those skilled in the art in light of the above teachings. . Therefore, it is to be understood that changes may be made in particular embodiments of the disclosed invention that fall within the scope and spirit of the invention as defined by the appended claims. Thus, while the present invention has been described in detail with the particularity and particularity required by the Patent Act, what is claimed and protected by Letters Patent is set forth in the appended claims.
[Brief description of the drawings]
FIG.
It is a figure showing a nanotube.
FIG. 2
It is a figure showing a hexagonal ring which constitutes a nanotube.
FIG. 3
It is a figure showing a hexagonal ring which constitutes a nanotube.
FIG. 4
It is a figure showing a multi-wall nanotube.
FIG. 5
FIG. 2 shows a single-wall nanotube rope.
FIG. 6
4 is a graph showing partial electrical breakdown of a multi-wall nanotube at a constant voltage over time.
FIG. 7
Figure 4 is a graph showing the alternation of low bias conductance between semiconducting and metallic behavior due to the outermost charge properties of the multi-wall nanotube at each stage of destruction.
FIG. 8
FIG. 5 is a graph showing the conductance of the semiconductive shell remaining after removing the last metallic shell from the multi-wall nanotube.
FIG. 9
It is a table | surface which shows the relationship of a shell number, a diameter, and a relative band gap energy.
FIG. 10
5 is a graph showing current (I) versus voltage of each shell of a multi-wall nanotube.
FIG. 11
FIG. 2 illustrates the transition from a random mixture of molecular conductors (nanotubes) to a semiconductive field effect transistor.
FIG.
FIG. 2 illustrates the transition from a random mixture of molecular conductors (nanotubes) to a semiconductive field effect transistor.
FIG. 13
FIG. 2 illustrates the transition from a random mixture of molecular conductors (nanotubes) to a semiconductive field effect transistor.
FIG. 14
FIG. 2 illustrates the transition from a random mixture of molecular conductors (nanotubes) to a semiconductive field effect transistor.
FIG.
It is a figure showing an electrode array.
FIG.
FIG. 2 illustrates a single-wall nanotube rope-based field effect transistor including a source, a drain and a gate.

Claims (12)

Preparing a substrate,
Forming a plurality of nanotubes in contact with the substrate;
A method for forming a device, comprising selectively destroying nanotubes using an electric current. The method of claim 1, wherein the substrate is an insulating substrate. The method of claim 1, further comprising depleting a plurality of carriers of the semiconductive nanotube. 4. The method of claim 3, wherein depleting the plurality of carriers of the semiconductive nanotube further comprises applying a voltage to a gate electrode on the substrate. 5. The method of claim 4, further comprising flowing the current from a source electrode to a drain electrode through the nanotube. The method of claim 1, wherein the plurality of nanotubes are single-wall nanotube ropes, including metallic and semiconductive nanotubes, or multi-wall nanotubes. 7. The method of claim 6, wherein selectively destroying comprises destroying an outer metallic nanotube, or destroying at least one metallic nanotube, or destroying a plurality of stray nanotubes. the method of. The method according to claim 1, wherein the nanotube is a carbon nanotube. A method of modifying at least one property of a nanotube, comprising:
Providing a mixture of nanotubes;
Passing a current through said mixture to induce selective destruction of said nanotube mixture. The method of claim 9, further comprising removing a plurality of carriers from the semiconductive nanotube. The method of claim 10, wherein the current selectively destroys the metallic nanotube. Providing an insulating substrate including a source electrode, a drain electrode and a gate electrode;
Providing a plurality of carbon nanotube bundles comprising metallic and semiconductive component nanotubes in contact with the substrate at a density of about 1 percent coverage;
Applying a voltage to the gate electrode to deplete the plurality of carriers of the semiconductive component nanotube;
Flowing a current from the source electrode to the drain electrode through the nanotube;
A method for forming a device, comprising the step of destroying at least one metallic component nanotube to form a field effect transistor.

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